1. Field of the Invention
The present invention relates to an illumination device for vehicles with at least one light-emitting diode and one light control unit, wherein the light control unit is connected to the at least one light-emitting diode and a pulse-width modulated clock signal can be generated and transmitted to the at least one light-emitting diode with the light control unit. Further, the invention relates to a method for controlling an illumination device for vehicles with at least one light-emitting diode and one light control unit.
2. Description of the Related Art
Light-emitting diodes are being used increasingly as light sources in vehicle lights. In particular, the light-emitting diode is becoming increasingly significant in the area of the exterior illumination of motor vehicles. These light sources have the advantage over conventional incandescent bulbs that they exhibit a longer lifetime and increased productive efficiency.
The light-emitting diodes are, for example, arranged in an array or several arrays. This way they can perform different illumination functions. There are illumination functions that differ with respect to brightness, i.e. the illumination functions differ with respect to the light flux emitted in the respective illumination functions. This way the same light-emitting diode or same light-emitting diode array can perform two or more illumination functions by emitting a different light flux in the different illumination functions.
Light-emitting diodes are conventionally controlled by way of a pulse-width modulated clock signal. The light flux, i.e. the brightness of the light-emitting diode is modified by way of the duty cycle of the clock signal, i.e. the ratio of the active to the passive phase is modified.
An illumination device for motor vehicles that exhibits as its light source light-emitting diodes, the brightness of which is adjustable, is known from DE 100 27 478 A1. The adjustment of the brightness is effected by modifying the duty cycle (pulse/pause ratio). A method for controlling illumination means in vehicles as well as a device for conducting a method in which the brightness of the light-emitting diodes is controlled by the pulse/pause ratio are also known from DE 199 45 546 A1.
A disadvantage of conventional controls of light-emitting diodes by means of the duty cycle of the pulse-width modulated clock signal is that the resolution of the modification in brightness, in particular at low levels of brightness, is too low. The duty cycle of the clock signal can usually be modified by 1% to 100% with a step size of at least 1%. Should the light-emitting diode not only perform two different illumination functions at different levels of brightness, but modify the brightness of one or several of the respective illumination functions with a very fine resolution, then the step sizes of known control devices are inadequate for light-emitting diodes.